Those in Year 11 at Plymouth College will self-isolate for 14 days after a student tested positive for coronavirus.
The pupil has not come into contact with anyone else outside their year bubble according to the school.
They added that those isolating will be taught online to ensure there is little impact on their education.
All other siblings, year groups and bubble groups are unaffected and have been asked to continue to attend school as normal.
Our careful preparations for the safe reopening of school included measures for what would happen in this case, and these are being put in place, guided by and working closely with Public Health England.
Mrs Jo Hayward, Headteacher at the school said: "Our Year 11 pupil has not come into close contact with anyone outside of the Year 11 bubble and as such, Year 11 will now remain at home for a period of 14 days.
"We will be delivering our full timetable of lessons for these students remotely, something we did successfully before the summer, to ensure there is little impact on their education.
"All other siblings, year groups and bubble groups are unaffected and should continue to attend school as normal.
"As ever, the health and safety of our staff and pupils is our priority and we have informed our school community of the confirmed case. Our staff will be available to support anyone with concerns."